Young H S, Skita V, Mason R P, Herbette L G
Department of Biochemistry, University of Connecticut, Farmington 06030-2017.
Biophys J. 1992 May;61(5):1244-55. doi: 10.1016/S0006-3495(92)81933-1.
The "membrane bilayer" pathway (Rhodes, D. G., J. G. Sarmiento, and L. G. Herbette. 1985. Mol. Pharmacol. 27:612-623.) for 1,4-dihydropyridine calcium channel drug (DHP) binding to receptor sites in cardiac sarcolemmal membranes has been extended to include the interaction of amphiphiles within the lipid bilayer. These studies focused on the ability of the Class III antiarrhythmic agents bretylium and clofilium to nonspecifically inhibit DHP-receptor binding in canine cardiac sarcolemma. Clofilium was found to inhibit nimodipine binding with an inhibition constant of approximately 5 microM, whereas bretylium had no effect on nimodipine binding. Small angle x-ray diffraction was then used to examine the differential ability of these two Class III agents to inhibit DHP-receptor binding. The time-averaged locations of bretylium, clofilium, and nimodipine in bovine cardiac phosphatidylcholine (BCPC) bilayers (supplemented with 13 mol% cholesterol) were determined to a resolution of 9 A. The location of bretylium as dominated by its phenyl ring in BCPC bilayers was found to be at the hydrocarbon core/water interface, similar to that of the dihydropyridine ring of nimodipine. The location of clofilium as dominated by its phenyl ring was found to be below the hydrocarbon/core water interface within the hydrocarbon chain region of the bilayer, similar to that of the phenyl ring of nimodipine. The location of the dihydropyridine ring portion of nimodipine has previously been shown by neutron diffraction to be located at the hydrocarbon core/water interface of native sarcoplasmic reticulum, consistent with the small angle x-ray data from model membranes in this paper. Therefore, we speculate that the nonspecific inhibition arises from the interaction of clofilium's phenyl ring with the site on the calcium channel receptor where the phenyl ring portion of nimodipine must interact. The DHP-receptor binding pathway would then involve both nonspecific (membrane) and specific (protein) binding components, both of which are necessary for receptor binding.
1,4 - 二氢吡啶类钙通道药物（DHP）与心肌肌膜中受体位点结合的“膜双层”途径（Rhodes, D. G., J. G. Sarmiento, and L. G. Herbette. 1985. Mol. Pharmacol. 27:612 - 623.）已得到扩展，以纳入脂质双层内两亲分子的相互作用。这些研究聚焦于Ⅲ类抗心律失常药物溴苄铵和氯非铵非特异性抑制犬心肌肌膜中DHP - 受体结合的能力。发现氯非铵抑制尼莫地平结合的抑制常数约为5微摩尔，而溴苄铵对尼莫地平结合无影响。然后使用小角X射线衍射来研究这两种Ⅲ类药物抑制DHP - 受体结合的差异能力。确定了溴苄铵、氯非铵和尼莫地平在牛心磷脂酰胆碱（BCPC）双层（补充13摩尔%胆固醇）中的时间平均位置，分辨率为9埃。发现溴苄铵在BCPC双层中以其苯环为主导的位置位于烃核/水界面，与尼莫地平的二氢吡啶环位置相似。发现氯非铵以其苯环为主导的位置位于双层烃链区域内烃核/水界面下方，与尼莫地平的苯环位置相似。尼莫地平二氢吡啶环部分的位置先前已通过中子衍射显示位于天然肌浆网的烃核/水界面，与本文中模型膜的小角X射线数据一致。因此，我们推测非特异性抑制源于氯非铵的苯环与钙通道受体上尼莫地平苯环部分必须相互作用的位点之间的相互作用。DHP - 受体结合途径将涉及非特异性（膜）和特异性（蛋白质）结合成分，两者对于受体结合都是必需的。
